(1) Field of the Invention
This invention relates to an optical switching device and, more particularly, to an optical switching device for switching an optical packet (optical signal).
(2) Description of the Related Art
Various systems are devised as next generation optical access networks for transmitting an optical signal to a subscriber system without converting the optical signal into an electrical signal. For example, a broadband passive optical network (B-PON) in which an asynchronous transfer mode (ATM) frame is sent, an Ethernet (registered trademark) passive optical network (E-PON) in which an Ethernet frame is sent, a GE-PON in which Gigabit Ethernet is applied, and the like are devised. International standardization project is being carried out.
Unlike active double star (ADS) networks in which active elements for performing an electrical/optical conversion are used, only passive optical components are used in these PON systems. Accordingly, end-to-end optical networks can be realized at low costs. The introduction of WDM-PONs in which a wavelength division multiplex (WDM) signal is used has also been examined in order to realize larger capacity.
Attention is riveted on a semiconductor optical amplifier (SOA), which is an optical element, in order to build a flexible optical wideband network. With an SOA, optical signal loss is light and high-speed switching is performed. By connecting SOAs at many stages as switching elements, an N×N switch with N inputs and N outputs can be formed. As a result, high-speed switching of an optical packet can be performed.
Conventionally, an optical switch including a demultiplexer for demultiplexing an optical signal into n signal components having different wavelengths, delay elements for assigning different delays to the demultiplexed signal components, and a wavelength conversion module for wavelength-converting the delayed signal components is proposed (see, for example, Japanese Patent Laid-Open Publication No. Hei11-146430, paragraph Nos. [0015]-[0019] and FIG. 1).
With a conventional N×N switch, however, an increase in the number of connection ports and the scale N of the switch causes a rapid increase in the number of necessary switching elements (SOAs) in proportion to the number of the connection ports. Therefore, it is difficult to miniaturize a device or reduce the costs of a device.
Furthermore, if a small-scale switch is installed at the beginning and is switched later to a large-scale switch at the time of an increase in the number of connections, it is difficult to smoothly upgrade the conventional N×N switch. It was necessary to replace a switch fabric section or the switch itself.